From 5e130c6d2ca4b99aedfbd6bb1198c32ac77e6ed6 Mon Sep 17 00:00:00 2001
From: Nathaniel Wesley Filardo <nfilardo@microsoft.com>
Date: Sat, 10 Dec 2022 11:14:50 +0000
Subject: [PATCH] StrictProvenance: deorbit metadata mixins

---
 .../cheri_slabmetadata_mixin.h                | 85 -------------------
 .../backend_helpers/defaultpagemapentry.h     | 15 +---
 2 files changed, 2 insertions(+), 98 deletions(-)
 delete mode 100644 src/snmalloc/backend_helpers/cheri_slabmetadata_mixin.h

diff --git a/src/snmalloc/backend_helpers/cheri_slabmetadata_mixin.h b/src/snmalloc/backend_helpers/cheri_slabmetadata_mixin.h
deleted file mode 100644
index 28e6f6ded..000000000
--- a/src/snmalloc/backend_helpers/cheri_slabmetadata_mixin.h
+++ /dev/null
@@ -1,85 +0,0 @@
-#pragma once
-#include "../pal/pal.h"
-
-namespace snmalloc
-{
-  /**
-   * In CHERI, we must retain, internal to the allocator, the authority to
-   * entire backing arenas, as there is no architectural mechanism to splice
-   * together two capabilities.  Additionally, these capabilities will retain
-   * the VMAP software permission, conveying our authority to manipulate the
-   * address space mappings for said arenas.
-   *
-   * We stash these pointers inside the SlabMetadata structures for parts of
-   * the address space for which SlabMetadata exists.  (In other parts of the
-   * system, we will stash them directly in the pagemap.)  This requires that
-   * we inherit from the FrontendSlabMetadata.
-   */
-  template<typename SlabMetadata>
-  class StrictProvenanceSlabMetadataMixin : public SlabMetadata
-  {
-    template<SNMALLOC_CONCEPT(IsPAL) A1, typename A2, typename A3, typename A4>
-    friend class BackendAllocator;
-
-    capptr::Arena<void> arena;
-
-    /* Set the arena pointer */
-    void arena_set(capptr::Arena<void> a)
-    {
-      arena = a;
-    }
-
-    /*
-     * Retrieve the stashed pointer for a chunk; the caller must ensure that
-     * this is the correct arena for the indicated chunk.  The latter is unused
-     * except in debug builds, as there is no architectural amplification.
-     */
-    capptr::Arena<void> arena_get(capptr::Alloc<void> c)
-    {
-      SNMALLOC_ASSERT(address_cast(arena) == address_cast(c));
-      UNUSED(c);
-      return arena;
-    }
-  };
-
-  /**
-   * A dummy implementation of StrictProvenanceBackendSlabMetadata that has no
-   * computational content, for use on non-StrictProvenance architectures.
-   */
-  template<typename SlabMetadata>
-  struct LaxProvenanceSlabMetadataMixin : public SlabMetadata
-  {
-    /* On non-StrictProvenance architectures, there's nothing to do */
-    void arena_set(capptr::Arena<void>) {}
-
-    /* Just a type sleight of hand, "amplifying" the non-existant bounds */
-    capptr::Arena<void> arena_get(capptr::Alloc<void> c)
-    {
-      return capptr::Arena<void>::unsafe_from(c.unsafe_ptr());
-    }
-  };
-
-#ifdef __cpp_concepts
-  /**
-   * Rather than having the backend test backend_strict_provenance in several
-   * places and doing sleights of hand with the type system, we encapsulate
-   * the amplification
-   */
-  template<typename T>
-  concept IsSlabMeta_Arena = requires(T* t, capptr::Arena<void> p)
-  {
-    {
-      t->arena_set(p)
-    }
-    ->ConceptSame<void>;
-  }
-  &&requires(T* t, capptr::Alloc<void> p)
-  {
-    {
-      t->arena_get(p)
-    }
-    ->ConceptSame<capptr::Arena<void>>;
-  };
-#endif
-
-} // namespace snmalloc
diff --git a/src/snmalloc/backend_helpers/defaultpagemapentry.h b/src/snmalloc/backend_helpers/defaultpagemapentry.h
index 034a2f0c5..2083db30e 100644
--- a/src/snmalloc/backend_helpers/defaultpagemapentry.h
+++ b/src/snmalloc/backend_helpers/defaultpagemapentry.h
@@ -1,7 +1,6 @@
 #pragma once
 
 #include "../mem/mem.h"
-#include "cheri_slabmetadata_mixin.h"
 
 namespace snmalloc
 {
@@ -65,19 +64,9 @@ namespace snmalloc
     SNMALLOC_FAST_PATH DefaultPagemapEntryT() = default;
   };
 
-  class StrictProvenanceSlabMetadata
-  : public StrictProvenanceSlabMetadataMixin<
-      FrontendSlabMetadata<StrictProvenanceSlabMetadata>>
+  class DefaultSlabMetadata : public FrontendSlabMetadata<DefaultSlabMetadata>
   {};
 
-  class LaxProvenanceSlabMetadata
-  : public LaxProvenanceSlabMetadataMixin<
-      FrontendSlabMetadata<LaxProvenanceSlabMetadata>>
-  {};
-
-  using DefaultPagemapEntry = DefaultPagemapEntryT<std::conditional_t<
-    backend_strict_provenance,
-    StrictProvenanceSlabMetadata,
-    LaxProvenanceSlabMetadata>>;
+  using DefaultPagemapEntry = DefaultPagemapEntryT<DefaultSlabMetadata>;
 
 } // namespace snmalloc